U.S. patent number 6,600,954 [Application Number 09/824,682] was granted by the patent office on 2003-07-29 for method and apparatus for selective control of nerve fibers.
This patent grant is currently assigned to Biocontrol Medical BCM Ltd.. Invention is credited to Shai Ayal, Ehud Cohen.
United States Patent |
6,600,954 |
Cohen , et al. |
July 29, 2003 |
Method and apparatus for selective control of nerve fibers
Abstract
A method and apparatus particularly useful for pain control by
selectively blocking the propagation of body-generated action
potentials travelling through a nerve bundle by using a tripolar
electrode device to generate unidirectional action potentials to
serve as collision blocks with the body-generated action potentials
representing pain sensations in the small-diameter sensory fibers.
In the described preferred embodiments there are a plurality of
electrode devices spaced along the length of the nerve bundle which
are sequentially actuated with delays corresponding to the velocity
of propagation of the body-generated action potentials through the
large-diameter fibers to produce a "green wave" effect which
minimizes undesired anodal blocking of the large-diameter fibers
while maximizing the collision blocking of the small-diameter
fibers.
Inventors: |
Cohen; Ehud (Ganei Tikva,
IL), Ayal; Shai (Jerusalem, IL) |
Assignee: |
Biocontrol Medical BCM Ltd.
(Yahnud, IL)
|
Family
ID: |
26950076 |
Appl.
No.: |
09/824,682 |
Filed: |
April 4, 2001 |
Current U.S.
Class: |
607/46 |
Current CPC
Class: |
A61N
1/36071 (20130101) |
Current International
Class: |
A61N
1/32 (20060101); A61N 1/34 (20060101); A61N
1/36 (20060101); A61N 001/34 () |
Field of
Search: |
;607/1,2,39-41,46,48,49,74,116-118 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4608985 |
September 1986 |
Crish et al. |
|
Foreign Patent Documents
Other References
Baratta et al, "Orderly Stimulation of Skeletal Muscle Motor Units
with Tripolar Nerve Cuff Electrode", IEEE Trans Biomed. Eng.,
38(8):836-843, 1989. .
Rattay, F., Analysis for Extracellular Fiber Stimulation, IEEE
Trans Biomed. Eng., 36(7):676-682, 1989. .
Rijkhoff et al, "Orderly Recruitment of Motoneurons in an Acute
Rabbit Model", IEEE Eng. In Medicine & Biol., 20(5):2564-2565,
1998. .
Rijkhoff et al, "Acute Animal Studies on the Use of an Anodal Block
to Reduce Urethral Resistance in Sacral Root Stimulation", IEEE
Rehabilitation Eng., 2(2):92-99, 1994. .
Fitzpatrick et al, "A Nerve Cuff Design for the Selective
Activiation and Blocking of Myelinated Nerve Fibres", IEEE Eng. In
Medicine & Biol., 13(2):0906-0907, 1991. .
Van Den Honert et al, "A Technique for Collision Block of
Peripheral Nerve: Single Stimulus Analysis", IEEE Trans Biomed.
Eng., BME-28(5):373-378, 1981. .
Devor, M., "Pain Networks", Handbook of Brain Theory and Neural
Networks. Ed. M.A. Arbib, MIT Press, pp 698-702, 1998..
|
Primary Examiner: Evanisko; George R.
Attorney, Agent or Firm: G. E. Ehrlich (1995) Ltd.
Parent Case Text
RELATED APPLICATION
This application is related to Provisional Application No.
60/263,834 filed Jan. 25, 2001, which is incorporated herein for
reference and claims priority of that application.
Claims
What is claimed is:
1. A method of reducing pain sensations resulting from the
propagation of body-generated action potentials towards the central
nervous system through small-diameter sensory fibers in a nerve
bundle, without unduly reducing other sensations resulting from the
propagation of body-generated action potentials towards the central
nervous system through large-diameter sensory fibers in said nerve
bundle, comprising: applying to said nerve bundle at least one
electrode device capable, upon actuation, of generating
unidirectional action potentials to be propagated through both the
small-diameter and large-diameter sensory fibers in said nerve
bundle away from said central nervous system; and actuating said
electrode device to generate said unidirectional action potentials
to produce collision blocks with respect to said body-generated
action potentials propagated through said small-diameter
fibers.
2. The method according to claim 1, wherein said electrode device
includes electrodes which: (a) generate said electrode-generated
action potentials by cathodic stimulation; (b) produce a complete
anodal block on one side of the cathode to make said
electrode-generated action potentials unidirectional; and (c)
produce a selective anodal block on the opposite side of the
cathode to cause the electrode-generated action potentials to
produce collision blocks with respect to the body-generated action
potentials propagated through the small-diameter sensory
fibers.
3. The method according to claim 2, wherein said electrode device
is a tripolar electrode device which includes a central cathode for
producing said cathodic stimulation, a first anode on one side of
the cathode for producing said complete anodal block, and a second
anode on the opposite side of said cathode for producing said
selective anodal block.
4. The method according to claim 1, wherein there are a plurality
of said electrode devices spaced along the length of the nerve
bundle; and wherein said electrode devices are sequentially
actuated with delays timed to the velocity of propagation of the
body-generated action potentials through said large-diameter fibers
to produce a "green wave" of electrode-generated anodal blocks,
thereby increasing the number of EGAPs in the small diameter fibers
producing collision blocks while minimizing anodal blocking of the
BGAPs propagated through the large-diameter sensory fibers.
5. A method of selectively suppressing the propagation of
body-generated action potentials propagated in a predetermined
direction at a first velocity through a first group of nerve fibers
in a nerve bundle without unduly suppressing the propagation of
body-generated action potentials propagated in said predetermined
direction at a different velocity through a second group of nerve
fibers in said nerve bundle, comprising: applying a plurality of
electrode devices to, and spaced along the length of, the nerve
bundle, each electrode device being capable of outputting, when
actuated, unidirectional electrode-generated action potentials
producing collision blocks with respect to the body-generated
action potentials propagated through said second type of nerve
fibers; and sequentially actuating said electrode devices with
delays timed to said first velocity to produce a "green wave" of
anodal blocks minimizing undesired blocking of said body-generated
action potentials propagated through said first group of nerve
fibers, while maximizing the generation rate of said unidirectional
electrode-generated action potentials producing collision blocks
with respect to the body-generated action potentials propagated
through said second type of nerve fibers.
6. The method according to claim 5, wherein said first group of
nerve fibers are large-diameter nerve fibers; and said second group
of nerve fibers are small-diameter nerve fibers.
7. The method according to claim 6, wherein said nerve fibers are
sensory nerve fibers, in which said predetermined direction of
propagation of the body-generated action potentials to be collision
blocked is towards the central nervous system, said method being
effective for suppressing pain sensations propagated through the
small-diameter sensory fibers without unduly suppressing other
sensations propagated through the large-diameter sensory
fibers.
8. The method according to claim 6, wherein said nerve fibers are
motor nerve fibers in which said predetermined direction of
propagation of the body-generated action potentials to be collision
blocked is away from the central nervous system towards a muscle or
gland, said method being effective for suppressing motor impulses
propagated through the small-diameter motor nerve fibers without
unduly suppressing the propagation of the motor impulses through
the large-diameter motor nerve fibers.
9. The method according to claim 5, wherein each of said electrode
devices is a tripolar electrode which includes a central cathode
for producing said electrode-generated action potentials by
cathodic stimulation, a first anode on one side of the cathode for
making said electrode-generated action potentials unidirectional,
and a second anode on the opposite side of said cathode for
producing a selective anodal blocking of said electrode-generated
action potentials.
10. A method of selectively controlling nerve fibers in a nerve
bundle having fibers of different diameters propagating action
potentials at velocities corresponding to their respective
diameters, comprising: applying a plurality of electrode devices
to, and spaced along the length of, the nerve bundle, each
electrode device being capable of producing, when actuated,
unidirectional electrode-generated action potentials; and
sequentially actuating said electrode devices with delays timed to
the velocity of propagation of action potentials through the fibers
of one of said diameters.
11. The method according to claim 10, wherein said electrode
devices are sequentially actuated to generate unidirectional action
potentials producing collision blocks of the body-generated action
potentials propagated through said nerve fibers of a another
diameter.
12. The method according to claim 11, wherein said electrode
devices are sequentially actuated with delays timed to the velocity
of the larger-diameter nerve fibers to produce a "green-wave" of
anodal blocks in order to minimize blocking the body-generated
action potentials propagated through the larger-diameter fibers
while maximizing the number of EGAPs collision blocking the
body-generated action potentials propagated through the small
diameter fibers.
13. The method according to claim 12, wherein said fibers include
large-diameter sensory fibers propagating body-generated action
potentials representing normal sensations from the peripheral
nervous system to the sensor nervous system, and small-diameter
sensory fibers propagating body-generated action potentials
representing pain sensations from the peripheral nervous system to
the central nervous system, which pain sensations in the
small-diameter sensory fibers are suppressed by collision block and
said "green-wave" of anodal blocks minimizes blocking of said
normal sensations in said large-diameter sensory nerves.
14. The method according to claim 12, wherein said nerve fibers
include large-diameter motor fibers propagating body-generated
action potentials representing certain motor controls from the
central nervous system to the peripheral nervous system, and
small-diameter motor nerve fibers representing other motor controls
from the central nervous system to the peripheral nervous system,
the motor controls in said small-diameter motor fibers being
suppressed by collision blocks and said green-wave of anodal blocks
minimizes blocking of the motor controls in said large-diameter
motor fibers.
15. The method according to claim 10, wherein said nerve fibers are
motor fibers of different diameters for propagating body-generated
action potentials from the central nervous system to the peripheral
nervous system, said electrode devices being sequentially actuated
to generate unidirectional action potentials to serve as motor
action potentials to be propagated from the central nervous system
to the peripheral nervous system to replace motor action potentials
failed to be generated by the body.
16. The method according to claim 10, wherein each of said
electrode devices is a tripolar electrode which includes a central
cathode for producing said electrode-generated action potentials by
cathodic stimulation, a first anode on one side of the cathode for
making said electrode-generated action potentials unidirectional,
and a second anode on the opposite side of said cathode for
producing a selective anodal blocking of said electrode-generated
action potentials.
17. Apparatus for blocking pain sensations resulting from the
propagation of body-generated action potentials towards the central
nervous system through a nerve bundle having small-diameter sensory
fibers and large-diameter sensory fibers, comprising: an electrical
device adapted to be applied to said nerve bundle and having at
least one electrode device capable, upon actuation, of generating
unidirectional action potentials to be propagated through both the
small-diameter and large-diameter sensory fibers in said nerve
bundle away from said central nervous system; and a stimulator
controlled to actuate said electrode device to generate said
unidirectional action potentials to produce collision blocks of the
body-generated action potentials in said small-diameter sensory
fibers such as to selectively block pain sensations resulting from
the propagation of body-generated action potentials towards the
central nervous system through said small-diameter sensory fibers
in the nerve bundle, without unduly reducing other sensations
resulting from the propagation of body-generated action potentials
towards the central nervous system through said large-diameter
sensory fibers in said nerve bundle; wherein said electrode device
includes electrodes which, when actuated by said stimulator: (i)
generate said electrode-generated action potentials by cathodic
stimulation; (ii) produce a complete anodal block on one side of
the cathode to make said electrode-generated action potentials
unidirectional; and (iii) produce a selective anodal block on the
opposite side of the cathode to block the electrode-generated
action potentials propagated through the large-diameter sensory
fibers to a greater extent than those propagated through the
small-diameter sensory fibers; wherein said electrode device is a
tripolar electrode which includes a central cathode for producing
said cathodic stimulation, a first anode on one side of the cathode
for producing said complete anodal block, and a second anode on the
opposite side of said cathode for producing said selective anodal
block; and wherein there are a plurality of said electrode devices
spaced along the length of the nerve bundle; and wherein said
electrode devices are sequentially actuated by said stimulator with
delays corresponding to the velocity of propagation of the
body-generated action potentials through said large-diameter fibers
to produce a "green wave" of electrode-generated action potentials
collision blocking with the body-generated action potentials
propagated through the small-diameter fibers while minimizing
anodal blocking of action potentials propagating through the
large-diameter fibers.
18. Apparatus for suppressing the propagation of body-generated
action potentials propagated at first and second velocities through
first and second types of nerve fibers in a nerve bundle,
comprising: a plurality of electrodes adapted to be spaced along
the length of the nerve bundle, each capable of producing, when
actuated, unidirectional electrode-generated action potentials and
a selective anodal block of the latter action potentials propagated
through said first type of nerve fibers to a greater extent than
those propagated through said second type of nerve fibers; and a
stimulator for sequentially actuating said electrode devices with
delays timed to said first velocity to produce a "green wave" of
anodal blocks minimizing undesired blocking of said body-generated
action potentials propagated through said first type of nerve
fibers, while maximizing the generation rate of said unidirectional
electrode-generated action potentials producing collision blocks
with respect to the body-generated action potentials propagated
through said second type of nerve fibers, such that the apparatus
selectively suppresses the propagation of body-generated action
potentials propagated at said first velocity through said first
type of nerve fibers in the nerve bundle without unduly suppressing
the propagation of body-generated action potentials propagated at
said second velocity through the second type of nerve fibers in
said nerve bundle.
19. The apparatus according to claim 18, wherein each of said
electrode devices is a tripolar electrode which includes a central
cathode for producing said electrode-generated action potentials by
cathodic stimulation, a first anode on one side of the cathode for
making said electrode-generated action potentials unidirectional,
and a second anode on the opposite side of said cathode for
producing said selective anodal blocking of said
electrode-generated action potentials, when said tripolar electrode
is a actuated by said stimulator.
20. The apparatus according to claim 19, wherein said plurality of
electrode devices and said stimulator are constructed to be
implanted into the subject's body with the electrodes in contact
with or closely adjacent to said nerve bundle.
21. The apparatus according to claim 19, wherein said apparatus
further includes an asynchronous, serial four-wire bus, and said
stimulator is connected to said plurality of electrode devices by
said asynchronous, serial four-wire bus.
22. The apparatus according to claim 19, wherein said apparatus
further includes a wireless communication link, and said stimulator
communicates with said plurality of electrode devices via said
wireless communication link.
23. The apparatus according to claim 19, wherein each of said
tripolar electrode devices includes an insulating base carrying
said cathode and said first and second anodes on one face thereof,
and control circuitry on the opposite face.
24. The apparatus according to claim 23, wherein said control
circuitry includes a microprocessor communicating with said
stimulator, and an L-C pulsing network controlled by said
microprocessor.
25. Apparatus for selectively controlling nerve fibers in a nerve
bundle having fibers of different diameters propagating action
potentials at velocities corresponding to their respective
diameters, comprising: a plurality of electrode devices adapted to
be applied to, and spaced along the length of, the nerve bundle,
each electrode device being capable of producing, when actuated,
unidirectional electrode-generated action potentials; and a
stimulator for sequentially actuating said electrode devices with
delays timed to the velocity of propagation of action potentials
through the fibers of one of said diameters.
26. The apparatus according to claim 25, wherein said stimulator
sequentially actuates said electrode devices to generate
unidirectional action potentials producing collision blocks of the
body-generated action potentials propagated through said nerve
fibers of another diameter.
27. The apparatus according to claim 26, wherein said stimulator
sequentially actuates said electrode devices with delays timed to
the propagation velocity of larger-diameter nerve fibers to produce
a "green-wave" of anodal blocks minimizing undesired blocking of
said body-generated action potentials propagated through the
large-diameter nerve fibers, while maximizing the generation rate
of said unidirectional electrode-generated action potentials
producing collision blocks with respect to the body-generated
action potentials propagated through the small diameter nerve
fibers.
28. The apparatus according to claim 25, wherein said nerve fibers
are motor fibers of different diameters for propagating
body-generated action potentials from the central nervous system to
the peripheral nervous system, and said stimulator sequentially
actuates said electrode devices to generate unidirectional action
potentials to serve as motor action potentials to be propagated
from the central nervous system to the peripheral nervous system to
replace motor action potentials failed to be generated by the body.
Description
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to the selective control of nerve
fibers in the human nervous system. The invention is especially
useful for selectively blocking sensory nerve fibers for blocking
pain sensations while permitting other sensations to pass, and is
therefore particularly described below with respect to this
application. However, as will also be described below the invention
could also be used in other applications, e.g., in selectively
blocking motor nerve fibers for controlling muscles or glands.
The nervous system is a network of billions of interconnected nerve
cells (neurons) that receive various types of stimuli and cause the
body to respond appropriately. The individual nerve cells transmit
the messages by means of a complicated electrochemical process
which generates action potentials transmitted by axons, or nerve
fibers. Such nerve fibers link the central nervous system (CNS)
consisting of the brain and the spinal cord, with the body's
receptors and effectors in the peripheral nervous system (PNS). The
receptors are sensory cells and organs responding to various types
of stimulation, such as touch, pain, light, etc., which transmit
action potentials through the sensory nerve fibers towards the CNS;
whereas effectors are parts of the body, such as muscles and
glands, that respond to instructions from the CNS transmitted via
action potentials through motor nerve fibers to effect a particular
activity in such muscles or glands.
Pain sensations have the useful purpose of alerting a person as to
a condition, such as heat or cold, which can be injurious to the
individual. However, there are many types of pains which do not
serve this useful purpose and can cause severe discomfort or
distress. For example, it is estimated that chronic pain partially
or totally disables 50 million persons in the USA alone, and that
45% of the population seeks medical help for persistent pain at
some point in their lives. Medical economists estimate that pain
costs the U.S. some $100 billion every year, including 515 million
workdays lost and 40 million doctors visits.
The most widely used controls for pain at the present time are
narcotic treatments. The narcotics most commonly prescribed not
only have a number of worrisome side effects, but are of limited
effectiveness for millions of persons who suffer from neuropathic
pain arising from damage to the nerves caused by disease, trauma or
chemotherapy.
Some degree of pain control may also be effected by electrical
stimulation. Current technology for pain control using electrical
stimulation is based on the "gate theory of pain"; see for example
M. Devor, "Pain Networks", Handbook of Brain Theory and Neural
Networks, Ed. M. A. Arbib, MIT Press, pp 698, 1998. This approach
exploits the observation that pain sensations diminish when
accompanied by a non-painful stimulus, such as the relief sensed
when rubbing a painful area. Pain sensations are carried by the
small-diameter nerve fibers (nociceptors), while normal sensations
(such as touch) are carried by the large-diameter nerve fibers. To
reduce pain, current techniques apply a low amplitude current which
stimulates only the large-diameter fibers, since stimulation of the
small-diameter fibers would induce pain. This is done in two ways:
(a) Transcutaneous Electric Stimulation (TENS) by applying a small
current externally to the skin; and (b) Dorals Column Stimulation
(DCS), by inserting an electrode into the dorsal column and
implanting a stimulating device nearby. This technique for pain
control, however, has had a very limited degree of success.
A number of blocking techniques are also presently known for
blocking or stimulating motor nerves controlling muscular or
glandular activities. These include: (1) collision blocking; (2)
high frequency blocking; and (3) anodal blocking.
In collision blocking, a unidirectional action potential is
generated by external electrodes to travel towards the muscle or
gland being controlled, i.e., from the CNS towards the PNS. These
electrode-generated action potentials collide with, and thereby
block, the body-generated action potentials.
In high frequency blocking, high frequency (e.g., 600 Hz)
stimulations are used to block the transmission of the action
potentials through the nerve fibers.
In anodal blocking, nerve fibers are locally hyper-polarized by
anodal current. If sufficiently hyper-polarized, action potentials
are not able to propagate through the hyper-polarized zone and will
be blocked.
As will be described more particularly below, the anodal block has
been investigated for producing a selective blocking of the action
potentials through selected motor nerve fibers, particularly the
larger-diameter nerve fibers which are more sensitive to the
hyper-polarization. The unblocked electrode-generated action
potentials (or those blocked to a lesser degree) passing through
the anodal block are used, by collision blocking, for the selective
control of motor nerve fibers in order to stimulate or suppress, as
the case may be, selected muscular or glandular activities; see for
example C. van den Honert, J. T. Mortimer "A Technique for
Collision Blocks of Peripheral Nerve: Single Stimulus Analysis",
IEEE Transactions on Biomedical Engineering, Vol. 28, No. 5, pp
373, 1981, herein incorporated by reference.
The anodal blocking technique has been investigated for stimulating
various motor nerves, e.g., for the restoration of bladder and
urethral sphincter control, for skeletal muscle control, etc.; see
for example D. M. Fitzpatrick et al., "A Nerve Cuff Design for the
Selective Activation and Blocking of Myelinated Nerve Fibers", Ann.
Conf. of the IEEE Eng. in Medicine and Biology Soc., Vol. 13, No.
2, pp. 906, 1991, describing a tripolar electrode device useful for
this purpose. Also see N. J. M. Rijkhof et al., "Acute Animal
Studies on the Use of Anodal Block to Reduce Urethral Resistance in
Sacral Root Stimulation" IEEE Transactions on Rehabilitation
Engineering, Vol. 2, No. 2, pp. 92, 1994; N. J. M. Rijkhoff et al.,
"Orderly Recruitment of Motoneurons in an Acute Rabbit Model" Ann.
Conf. of the IEEE Eng., Medicine and Biology Soc., Vol. 20, No. 5,
pp. 2564, 1998; and R. Bratta et al., "Orderly Stimulation of
Skeletal Muscle Motor Units with Tripolar Nerve Cuff Electrode",
IEEE Transactions on Biomedical Engineering, Vol. 36, No. 8, pp.
836, 1989. The contents of the foregoing publications are
incorporated herein by reference.
As described particularly in the above-cited Fitzpatrick et al
publication, the tripolar electrode used for muscle control
includes a central cathode flanked on its opposite sides by two
anodes. The central cathode generates action potentials in the
motor nerve fiber by cathodic stimulation; one anode produces a
complete anodal block in one direction so that the action potential
produced by the cathode is unidirectional; and the other anode
produces a selective anodal block to permit passage of the action
potential in the opposite direction through selected motor nerve
fibers to produce the desired muscle stimulation or suppression.
Further details concerning the construction and operation of such
tripolar electrodes are set forth in the above-cited publications
incorporated herein by reference.
OBJECTS AND BRIEF SUMMARY OF THE PRESENT INVENTION
An object of the present invention is to provide novel methods of
selective control of nerve fibers which method is particularly
useful for reducing pain sensations. Another object is to provide a
method of selectrive control of nerve fibers which is also useful
for controlling certain types of muscular or glandular activities.
A further object of the invention is to provide apparatus for use
in the above methods.
According to one aspect of the present invention, there is provided
a method of reducing pain sensations resulting from the propagation
of body-generated action potentials towards the central nervous
system through small-diameter sensory fibers in a nerve bundle,
without unduly reducing other sensations resulting from the
propagation of body-generated action potentials towards the central
nervous system through large-diameter sensory fibers in the nerve
bundle, comprising: applying to the nerve bundle at least one
electrode device capable, upon actuation, of generating
unidirectional action potentials to be propagated through both the
small-diameter and large-diameter sensory fibers in the nerve
bundle away from the central nervous system; and actuating the
electrode device to generate the unidirectional action potentials
to produce collision blocks with respect to the body-generated
action potentials propagated through the small-diameter fibers.
Preferably, this aspect of the invention utilizes the tripolar
electrode devices described, for example, in the above-cited
publications, except that, instead of using such tripolar
electrodes for producing collision blocks of action potentials
travelling through motor nerves away from the central nervous
system in order to control muscular or glandular activity, there
are used to produce collision blocks of action potentials
propagated through sensory nerves towards the central nervous
system in order to reduce pain sensations without unduly hindering
other sensations.
According to another aspect of the present invention, there is
provided a method of selectively suppressing the propagation of of
body-generated action potentials propagated in a predetermined
direction at a first velocity through a first group of nerve fibers
in a nerve bundle without unduly suppressing the propagation of
body-generated action potentials propagated in the predetermined
direction at a different velocity through a second group of nerve
fibers in the nerve bundle, comprising: applying a plurality of
electrode devices to, and spaced along the length of, the nerve
bundle, each electrode device beams capable of outputting, when
actuated, unidirectional electrode-generated action potentials
producing collision blocks with respect to the body-generated
action potentials propagated through the second type of nerve
fibers; and sequentially actuating the electrode devices with
delays timed to the first velocity to produce a "green wave" of
anodal blocks minimizing undesired blocking of the body-generated
action potentials propagated through the first group of nerve
fibers while maximizing the generation rate of said unidirectional
electrode-generated action potentials producing collision blocks
with respect to the body-generated action potentials propagated
through said second type of nerve fibers.
Such a method may be used for producing collision blocks in sensory
nerve fibers in order to suppress pain, and also in motor nerve
fibers to suppress selected muscular or glandular activities.
According to a further aspect of the invention, there is provided a
method of selectively controlling nerve fibers in a nerve bundle
having fibers of different diameters propagating action potentials
at velocities corresponding to their respective diameters,
comprising: applying a plurality of electrode devices to, and
spaced along the length of, the nerve bundle, each electrode device
being capable of producing, when actuated, unidirectional
electrode-generated action potentials; and sequentially actuating
the electrode devices with delays timed to the velocity of
propagation of action potentials through the fibers of one of the
diameters.
In some described preferred embodiments, the electrode devices are
sequentially actuated to generate unidirectional action potentials
producing collision blocks of the body-generated action potentials
propagated through the nerve fibers of another diameter. Such
collision blocks may be used for suppressing pain sensations
without unduly interfering with normal sensations, or for
selectively suppressing certain motor controls without unduly
interfering with others.
According to still further aspects of the present invention, there
is provided apparatus for use in the above methods.
Further features and advantages of the invention will be apparent
from the description below.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is herein described, by way of example only, with
reference to the accompanying drawings, wherein:
FIG. 1 illustrates the construction and mode of operation of a
tripolar electrode device particularly useful in the present
invention;
FIG. 2 diagrammatically illustrates an array of tripolar electrode
devices constructed in accordance with the present invention for
selectively blocking the propagation through certain nerve-fibers
of body-generated action potentials;
FIG. 3 is a block diagram illustrating the stimulator in the
apparatus of FIG. 2;
FIG. 4 is a block diagram illustrating the operation of the
apparatus of FIGS. 2 and 3 for suppressing pain sensations;
FIGS. 5a and 5b are block diagrams illustrating how the apparatus
of FIGS. 2 and 3 may also be used for suppressing selected muscular
or glandular activities controlled by the motor nerves;
FIGS. 6a and 6b are block diagrams illustrating how the apparatus
of FIGS. 2 and 3 may also be used for stimulating selected motor or
glandular activities upon the failure of the body to generate the
required action potentials;
FIGS. 7a and 7b are diagrams helpful in explaining the manner of
calibrating the apparatus of FIGS. 2 and 3;
FIG. 8 illustrates one form of assembly of a plurality of tripolar
electrode devices constructed in accordance with the present
invention for use in the apparatus of FIGS. 2 and 3;
FIG. 9 diagrammatically illustrates the manner of controlling the
electrode devices in the assembly of FIG. 5 by means of an
asynchronous serial four-wire bus;
FIG. 10 is an electrical diagram schematically illustrating the
construction of one of the tripolar electrode devices used in the
assembly of FIGS. 8 and 9;
FIGS. 11a, 11b and 11c are side, plan and end views, respectively,
diagrammatically illustrating the construction of one of the
tripolar electrode devices used in the electrode assembly of FIGS.
8 and 9;
FIG. 12 illustrates the electrode assembly of FIGS. 8 and 9 applied
for blocking the propagation of body-generated action potentials in
the sciatic nerve fiber in the leg of a subject; and
FIG. 13 illustrates the electrode assembly of FIGS. 8 and 9 applied
for blocking the propagation of body-generated action potentials
through two nerve fibers in the arm of a subject.
DESCRIPTION OF PREFERRED EMBODIMENTS
The Tripolar Electrode
A basic element in the preferred embodiments of the method and
apparatus described below is the tripolar electrode device. Its
construction and operation are diagrammatically illustrated in FIG.
1.
As shown in FIG. 1, the tripolar electrode device, therein
designated 10, includes three electrodes, namely, a central cathode
11, a first anode 12 on one side of the cathode, and a second anode
13 on the opposite side of the cathode. The illustrated tripolar
electrode device further includes a microcontroller 14 for
controlling the three electrodes 11, 12 and 13, as will be
described below.
Curve 15 shown in FIG. 1 illustrates the activation function
performed by the tripolar electrode device 10 on the nerve bundle
underlying it. As shown in FIG. 1, this activation function
includes a sharp positive peak 15a underlying the cathode 11, a
relatively deep negative dip 15b underlying the anode 12, and a
shallower negative dip 15c underlying the anode 13.
When the tripolar electrode 10 is placed with its cathode 11 and
anodes 12, 13 in contact with, or closely adjacent to, a nerve
bundle, the energization of the cathode 11 generates, by cathodic
stimulation, action potentials in the nerve bundle which are
propagated in both directions; the energization of anode 12
produces a complete anodal block to the propagation of the
so-generated action potentials in one direction; and the
energization of anode 13 produces a selective anodal block to the
propagation of the action potentials in the opposite direction.
It is known that large-diameter nerve fibers have low excitation
thresholds and higher conduction velocities than progressively
smaller-diameter nerve fibers; and therefore the tripolar electrode
device can generate unidirectional action potentials in the
small-diameter fibers while blocking in the large-diameter fibers.
It is also known that changing the ratio of the anodal currents can
produce gradual recruitment of the large fibers; see for example
the above-cited Fitzpatrick et al and Bratta et al publications,
incorporated herein by reference. However, whereas this technique
is described in the above-cited publications for producing
collision blocks of action potentials propagated from the central
nervous system via motor fibers in order to stimulate or suppress
muscular or glandular activity, in the present invention, according
to one aspect, this technique is used for pain control by blocking
pain sensations propagated towards the central nervous system in
small-diameter sensory fibers without unduly hindering normal
sensations propagated through the large-diameter sensory
fibers.
According to another aspect of the present invention, a plurality
of electrode devices, preferably of such tripolar electrodes, are
used to generate a sequence of electrode-generated action
potentials (EGAPs) for more effectively suppressing the propagation
of body-generated action potentials (BGAPs) propagated through
sensory nerves towards the central nervous system (CNS) for pain
control, as well as for suppressing the propagation of
body-generated action potentials propagated through motor nerves
from the central nervous system towards the peripheral nervous
system (PNS) for muscular or glandular stimulation or suppression.
As will be described more particularly below, the plurality of
electrode devices are sequentially actuated with delays to produce
a "green wave" of unidirectional EGAPs effective to reduce the
interference with the BGAPs propagated unhindered, or to reinforce
the stimulation of muscular or glandular activities desired to be
effected.
The Overall Apparatus
FIGS. 2 and 3 are diagrams illustrating one form of apparatus
constructed in accordance with the present invention utilizing a
plurality of the tripolar electrode devices, therein designated
10a-10n, shown in FIG. 1. Such electrode devices are interconnected
by a bus 16 to form an electrode array 18 to be applied, as by
implantation, with the electrode devices spaced along the length of
the nerve bundle, shown at 19, and to be selectively actuated, as
will be described more particularly below, by a stimulator,
generally designated 20. The construction of the stimulator 20 is
more particularly illustrated in FIG. 3.
Each of the electrode devices 10a-10n is of the tripolar
construction shown in FIG. 1, to include a central cathode 11
flanked on its opposite sides by two anodes 12, 13. Each such
electrode device further includes a microcontroller, shown at 14 in
FIG. 1, and more particularly described below with respect to FIG.
7, for sequentially controlling the actuation of the electrodes
11-13 of each electrode device in order to produce the "green wave"
briefly described above, and to be more particularly described
below.
The assembly of electrode devices 10a-10n, and the stimulator 20
for sequentially actuating them, are preferably both implantable in
the body of the subject with the electrodes in contact with, or
closely adjacent to, the nerve bundle 15. Accordingly, the
simulator 20 includes its own power supply, shown at 22 in FIG. 3.
The stimulator 20 further includes a microcontroller 23 having
output stage 24 connected, via connector block 25, to the plurality
of electrode devices 10a-10n for sequentially actuating them, as
will be described below.
Stimulator 20 further includes an input circuit for inputting
various sensor signals for purposes of calibration and/or control.
As shown in FIG. 3, such inputs may be from an EMG (electromyogram)
signal sensor 26a and from an accelerator sensor 26b. The EMG
sensor 26a may be used for calibration purposes, e.g., to calibrate
the apparatus according to EMG signals generated by a subject's
muscle during the calibration of the apparatus (described below),
or for control purposes, e.g., for automatically actuating the
device upon the occurrence of a particular EMG signal. The
accelerator sensor 26b may be used for control purposes, e.g., to
automatically actuate the device upon the occurrence of tremors or
spasms in order to suppress in the tremors by blocking certain
motor nerves.
Stimulator 20 may also have an input from a perspiration sensor 26c
for automatic control of sweat glands. It may also have an input
from one of the electrodes serving as a reference electrode for
calibration purposes, as will also be described more particularly
below.
The inputs into the stimulator 20 may be by wire or bus, as shown
at 27 in FIG. 3. Such inputs are amplified in amplifier 28, and
digitized in a digitizer 29, before being inputted into the
microcontroller 23.
The inputs to the stimulator 20 may also be by wireless
communication, as schematically shown at 30 in FIG. 3, particularly
where the device is implanted. For this purpose, stimulator 20
includes a receiver 31 for receiving such inputs. Such inputs are
also amplified in amplifier 28 and digitized in digitizer 29 before
being inputted into the microcontroller 23.
Operation of the Illustrated Apparatus
The apparatus illustrated in FIGS. 2 and 3, when applied along the
length of the nerve bundle 15 as shown in FIG. 2, is capable of
suppressing the propagation of body-generated action potentials
(BGAPs) propagated through the small-diameter nerve fibers in a
nerve bundle without unduly suppressing the propagation of BGAPs
propagated through the large-diameter nerve fibers in the nerve
bundle. One application of such a device is to reduce pain
sensations; and another application of the device is to suppress
muscular or glandular activities. The apparatus illustrated in
FIGS. 2 and 3 may also be used for generating, by the electrode
devices, action potentials (hereinafter frequently referred to as
electrode-generated action potentials, or EGAPS) where the body
fails to produce the necessary BGAPs to produce a particular
muscular or glandular activity. A further application of the
apparatus, therefore, is to stimulate a muscular or glandular
activity.
As described above, when the cathode 11 of each tripolar electrode
device 10 is actuated, it generates an action potential by cathodic
stimulation propagated in both directions; whereas when anode 12 of
the respective tripolar electrode 10 is energized, it produces a
complete anodal block on one side of the cathode, to thereby make
the electrode-generated action potential unidirectional and
propagated away from the central nervous system. On the other hand,
when anode 13 is energized, it produces an anodal block only with
respect to the BGAPs propagated through the large-diameter sensory
nerves, since they are more sensitive to the anodal current.
Accordingly, the EGAPs from the small-diameter sensory nerves are
permitted, to a larger extent, to propagate through the anodal
block.
The EGAPs outputted by the anodal block may be used as collision
blocks with respect to sensory BGAPs to suppress pain, or with
respect to motor BGAPs to suppress undesired muscular activity
(e.g., tremors, spasms), or glandular activity (e.g., excessive
perspiration).
An undesired side effect of this activation scheme, is that at the
time when anode 12 of device 10 is actuated to generate an anodal
block as described above, all BGAPs in both small and large fibers
are blocked and cannot pass the device. Thus every production of an
EGAP is accompanied by a brief period in which all BGAPs cannot
pass the site of the device 10. In order to minimize the blocking
of BGAPs while maximizing the amount of EGAPs produced, the
tripolar electrode devices 10a-10n are sequentially actuated, under
the control of the stimulator 20. This sequential actuation is
timed with the propagation velocity of the action potentials
through the nerve fiber not to be blocked. Thus, as well known for
controlling vehicular traffic, when stop lights spaced along a
thoroughfare are controlled to define a "green wave" travelling at
a predetermined velocity, the vehicles travelling at the "green
wave" velocity will be less hindered than if the stop lights were
not synchronized with their velocity.
The anodal blocks produced by the sequential actuation of the
tripolar electrodes are comparable to the stop lights in a
thoroughfare, and therefore the action potentials travelling at the
velocity of the green wave will be less hindered by such stop
lights or anodal blocks.
Thus, where the invention is used for pain control by suppressing
the BGAPs in the small-diameter sensory nerves, producing a "green
wave" of anodal blocks timed with the conduction velocity through
the large-diameter sensory nerves, there will be less interference
with the BGAPs representing normal sensations, travelling through
the large-diameter sensory nerve fibers, as compared to the BGAPs
representing pain sensations travelling through the small-diameter
sensory nerve fibers which will be collision blocked by the
EGAPs.
The same "green wave" effect can be provided in order to suppress
BGAPs propagating through motor nerve fibers in order to block
motor controls of selected muscles or glands.
Examples of Use of the Apparatus
FIG. 4 illustrates an example of use of the described apparatus for
reducing pain sensations by suppressing the BGAPs transmitted
through the small-diameter sensory fibers without unduly hindering
the transmission of the BGAPs through the large-diameter sensory
fibers.
Thus, as shown in FIG. 4, the BGAPs in the peripheral nervous
system PNS (block 40) generate normal sensations in the large
sensory fibers 41 and pain sensations in the small sensory fibers
42. Normally, both types of sensations are propagated through their
respective fibers to the central nervous system (CNS, block
43).
However, as shown in FIG. 4, the assembly of electrodes 10a-10n,
when sequentially actuated with delays timed to the conduction
velocity of the large-diameter fibers 41, generates unidirectional
EGAPs (block 44) which are outputted with delays timed to
correspond to the velocity of the large sensory fibers (as shown at
45) to produce a collision block (46) with respect to the BGAPs
propagated through the small sensory fibers (42) without unduly
hindering the BGAPs propagated through the large sensory fibers 41
to the central nervous system 43. Accordingly, the pain sensations
normally propagated through the small sensory fibers 42 to the
central nervous system 43 will be suppressed, while the normal
sensations propagated through the large sensory fibers 41 will
continue substantially unhindered to the central nervous
system.
In addition, as shown by line 47 in FIG. 4, the motor action
potentials from the CNS to the PNS are also substantially
unhindered.
FIGS. 5a and 5b illustrate the application of the apparatus for
suppressing certain muscular or glandular activities normally
controlled by the BGAPs transmitted through the motor nerve fibers.
In this case, as shown in FIG. 5a, the BGAPs are generated in the
central nervous system (block 50) and are normally transmitted via
large motor fibers 51 and small motor fibers 52 to the peripheral
nervous system 53. FIG. 5a illustrates the arrangement wherein the
EGAPs are generated at a rate corresponding to the velocity of the
large motor fibers, as shown by blocks 54 and 55, so that they
produce collision blocks with respect to the small motor fibers 52,
and permit the BGAPs to be transmitted through the large motor
fibers 51 to the peripheral nervous system 53.
FIG. 5b illustrates the variation wherein the apparatus generates
EGAPs at a rate corresponding to the velocity of the small motor
fibers (blocks 54, 55), such that the collision blocks (56) block
the large motor fibers 51, and permit the BGAPs to be transmitted
to the peripheral nervous system 53.
FIGS. 6a and 6b illustrate the applications of the apparatus for
stimulating a particular muscle or gland where the body fails to
develop adequate BGAPs in the respective motor nerve fiber for the
respective muscular or glandular control. In this case, the
apparatus generates unidirectional EGAPs selectively for the
respective muscle or gland.
FIG. 6a illustrates the application of the invention wherein the
body fails to generate in the central nervous system 60 adequate
BGAPs for transmission by the large motor fibers to the peripheral
nervous system 63, in which case the electrode devices 10a-10n in
the electrode assembly would be sequentially energized by the
stimulator 64 with delays timed to the velocity of propagation of
action potentials through the large motor fibers. The
unidirectional EGAPs are thus produced with delays timed to the
conductive velocity of the large motor fibers, thereby permitting
them to be transmitted via the large motor fibers to the peripheral
nervous system.
FIG. 6b, on the other hand, illustrates the case where the
electrodes 10a-10n are sequentially energized with delays timed to
the velocity of the small motor fibers, thereby permitting the
unidirectional EGAPs to be outputted via the small-diameter fibers
to the peripheral nervous system 63.
Calibration
For best results, each electrode assembly should be calibrated for
each patient and at frequent intervals. Each calibration requires
adjustment of the cathodic and anodic currents in each tripolar
electrode, and also adjustment of the timing of the sequential
actuation of the tripolar electrodes.
To calibrate the cathodic and anodic currents for each electrode,
the proximal electrode (10a, FIG. 2) is actuated to produce a
unidirectional action potential propagated towards the distal
electrode (10n) at the opposite end of the array. The so-produced
action potential, after having traversed all the electrodes between
electrodes 10a, and 10n, is detected and recorded by the distal
electrode 10n. The currents in the electrodes are iteratively
adjusted to produce maximum blocking.
FIG. 7a illustrates, at "a", the signal detected by the distal
electrode when the blocking is minimum, and at "b" when the signal
detected by the distal electrode when the blocking is maximum.
FIG. 7b illustrates the manner of calibrating the electrode array
to produce the proper timing in the sequential actuation of the
electrodes for calibrating the sequential timing, the proximate
electrode (10a) is again actuated to produce a unidirectional
action potential propagated toward the distal electrode (10n). As
the so-produced action potential traverses all the electrodes
inbetween, each such inbetween electrode detects and records the
action. This technique thus enables calibrating the electrode array
to produce the exact delay between the actuations of adjacent
electrodes to time the sequential actuations with the conduction
velocity of the respective nerve fiber.
For example, where the sequential actuation is to produce a "green
wave" having a velocity corresponding to the conduction velocity of
the large sensory nerve fibers for reducing pain sensations, the
timing would be adjusted so as to produce the sequential delay
shown in FIG. 7b to thereby time the sequential actuations of the
electrodes to the conductive velocity in the large sensory
fibers.
The EMG sensor 26a shown in FIG. 3 may also be used for calibrating
the electrode currents and sequential timing when the apparatus is
to be used for providing a stimulation of a muscular or glandular
activity where the body fails to provide the necessary BGAPs for
this purpose. In this case, the currents and timing would be
adjusted to produce a maximum output signal from the EMG sensor 26a
for the respective muscle.
The EMG sensor 26a could also be used to automatically actuate the
apparatus upon the detection of an undesired EMG signal, e.g., as a
result of a tremor or spasm to be suppressed. For example, the
accelerator sensor 26b could be attached to a limb of the subject
so as to automatically actuate the apparatus in order to suppress
tremors in the limb upon detection by the accelerator.
Other sensors could be included, such as an excessive perspiration
sensor 26c, FIG. 3. This would also automatically actuate the
apparatus to suppress the activity of the sweat glands upon the
detection of excessive perspiration.
A Preferred Electrode Array Construction
FIGS. 8 and 9 illustrate a preferred construction for the electrode
array 18, including the plurality of tripolar electrode devices
10a-10n interconnected by bus 16 and connected to the stimulator
20. In this preferred construction, as shown in FIG. 9, the bus 16
interconnecting the tripolar electrodes 10a-10n is an asynchronous
serial four-wire bus. Such an arrangement may use the well-known
JTAG/IEEE 1149.1 Protocol, in which a four-wire bus (as shown at
Vcc, TX, RX and GND, FIG. 10) carries the data to all the electrode
devices connected in serial. In such case, the microcontroller
circuitry (14, FIG. 1) in each tripolar electrode device 10 would
include a JTAG controller 14a acting as a communication processor,
and a stimulation processor 14b. The communication processor 14a
processes the commands issued by the stimulator microcontroller 20
and passes any relevant commands to the stimulation processor 14b
of the respective tripolar electrode device. This enables two-way
communication between the stimulator controller and each tripolar
electrode device utilizing only four wires.
Instead of using the JTAG/IEEE 1149.1 Protocol or other
asynchronous four wires bus wireless communication may also be used
by using an established wireless protocol, e.g., Bluetooth.
Wireless communication can be advantageous if the stimulator
microcontroller 20 is separated from the electrode array 18 in
order to avoid the possibility of mechanical breakage of long
electrode leads.
A Preferred Tripolar Electrode Construction
FIG. 10 diagrammatically illustrates a preferred electrical
construction, and FIGS. 11a-11c diagrammatically illustrate a
preferred physical construction, for each of the tripolar
electrodes 10 included in the electrode array 18 of FIG. 2.
Thus, FIG. 10 illustrates the four-wire connections to the
communication processor 14a briefly described above. As also seen
in FIG. 10, each tripolar electrode further includes a capacitor C
(e.g., at least 10 .mu.F, preferably 20 .mu.F), and a coil L (e.g.,
at least 50 .mu.H, preferably 68 .mu.H) connected to the
communication processor and defining a pulsing circuit for pulsing
the electrodes 11, 12, 13 controlled by the communication
processor.
The physical construction of each of the tripolar electrode devices
is shown by the diagrammatic side view 11a, plan view 11b, and end
view 11c.
Thus, as shown in these views, each tripolar electrode device
includes a to silicon substrate 70 within a sleeve 71 formed with
the three electrodes 11, 12, 13 as longitudinally-spaced conductive
strips on one face to be brought into direct contact, or very close
proximity, to the nerve bundle. The silicon substrate 70 carries
the electrical circuitry (14, FIG. 1) including the microcontroller
14a, the capacitor C, and coil L of the respective pulsing network.
The silicon substrate 70 further includes conductive deposits
(e.g., nickel) 72 for connection to the four wires of the bus (as
shown in FIG. 10), and further conductive deposits (e.g., nickel)
73 for connection to the three electrodes 11, 12, 13.
An example of the various dimensions in the construction of each
tripolar electrode is shown in FIGS. 11a-11c.
Example of Use of the Apparatus
FIG. 12 illustrates the apparatus as including one electrode array
18 powered by one stimulator 20 both implanted in the leg of a
subject for suppressing pain originating from the sciatic
nerve.
FIG. 13 illustrates two electrode arrays, shown as 18a, 18b,
implanted in the arm of the subject and both powered by a common
stimulator 20 also implanted in the subject.
While FIGS. 12 and 13 illustrate the apparatus as implanted in the
body of the subject, in some applications it may be preferable to
apply the apparatus externally of the subject's body and make
connections from the electrodes to the respective nerve bundle.
Accordingly, while the invention has been described with respect to
several preferred embodiments, it will be appreciated that these
are set forth merely for purposes of example, and that many other
variations, modifications and applications of the invention may be
made.
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